Preserve MCP resource origins across compaction (#39192)

## Why

Compaction can remove the tool-call events that associate an MCP app widget with
the tool, account, and URI needed to authorize later resource reads.

## What changed

- Store a bounded MCP resource-origin checkpoint with each compacted rollout.
- Restore the checkpoint when resuming a session so existing widgets remain
  readable after compaction and restart.
- Discard saved origins when rollback rewrites history across the compaction
  boundary, and reject oversized or invalid checkpoints during restoration.

## Testing

- Extend the app-server MCP resource-origin test to compact a paginated thread,
  continue the conversation, and read the original widgets before and after a
  restart.
- Verify rollback clears provenance that no longer matches retained history.

GitOrigin-RevId: 7f91c6202fe8d9be21c78dda42fa205937c44263

codex-rs/core/src/session/mod.rs

@@ -3334,6 +3334,7 @@ impl Session {
         let compacted_item = CompactedItem {
             message: metadata.message,
             replacement_history: Some(items.clone()),
+            mcp_resource_origins: self.services.mcp_runtime.resource_origin_checkpoint(),
             window_number: Some(metadata.window_number),
             first_window_id: Some(metadata.window_ids.first_window_id.to_string()),
             previous_window_id: metadata